The subject of the present invention is a process and a device for manufacturing a reinforced composite article.
In many industrial fields, composite articles are used consisting of a solid plastic-based body reinforced by means of reinforcing fibres such as glass fibres. These reinforcing fibres may especially be employed in the form of bundles of continuous fibres, these bundles being impregnated with a thermoplastic. It is thus possible to manufacture, for example, bars, rods, longerons, beams, sections, etc., reinforced by bundles of continuous fibres, these bundles being wound at their surface and these articles having a low weight and a high mechanical strength.
Currently, these plastic-based reinforced composite articles are manufactured by firstly extruding a plastic solid body. This solid body is then sized and then possibly reheated in order to soften its outer surface layer. One or more reinforcing tapes, generally comprising reinforcing fibres, for example glass fibres impregnated with a thermoplastic, are then wound round the solid body. This winding is performed, for example, by means of a device for winding the reinforcing tapes rotating around the solid body while the latter runs axially through this winding device. The speed of rotation of this device is regulated as a function of the running speed of the solid body so as to determine the pitch of the winding.
A first process for ensuring sufficient contact pressure of the reinforcing tape or tapes on the solid body consists, when winding the reinforcing tape, in exerting a large tensile force on this tape. This tensile force must especially create a suitable pressure between the reinforcing tape and the solid body. Control equipment can adjust the tensile force exerted on the reinforcing tape, but the effective contact pressure, however, is not easily quantifiable since it depends not only on the tensile force exerted on the reinforcing tape, but also on the contact conditions, especially on the deformations of the surface layer of the solid body and/or of the reinforcing tape due to the effect of the tensile force. If the tensile force required for ensuring good adhesion of the wound reinforcing tape is too great, it generates large deformations of the reinforcing tape, for example a regrouping of the fibres lying within the reinforcing tape towards the centre of the latter and creep of the plastic impregnating it towards its periphery. In extreme cases, the article may be deformed and/or the reinforcing tape may penetrate deeply into the solid body. In addition, the surface finish of the articles obtained by this process is often poor, therefore making it especially difficult to deposit the optional finishing layer.
Another process for ensuring sufficient contact pressure between the reinforcing tape and the solid body consists in applying a local pressure on the reinforcing tape in the region of the area of first contact between the reinforcing tape and the solid body. For this purpose, a cooled compression block is arranged at the very point of the first contact between the reinforcing tape and the solid body. The contact pressure, which is thus largely independent of the tensile force exerted on the reinforcing tape, becomes more easily controllable. It is consequently applied more uniformly and the surface finish of the article is improved. However, the compression block must be maintained at a sufficiently low temperature to prevent the plastic from adhering to it. In this process, it is therefore very important to maintain the temperature of the contact surface of the block below a critical value. This critical temperature depends, among other things, on the nature of the plastic constituting, covering or impregnating the reinforcing tape. In general, it is below room temperature. The result of this is that the reinforcing tape, which moreover has a very low thermal inertia, is immediately on contact with the pressure block. It is consequently impossible to have an optimum temperature of the reinforcing tape--that is to say an optimum viscosity of the plastic which impregnates it--at the point where it is applied to the softened surface of the solid body. In conclusion, this process does not really enable conditions to be obtained which favour good adhesion between the reinforcing tape and the solid body.